Hair dye compositions can be classified according to the presence or absence of a bleaching action against the dye used or melanin. Representative examples of the hair dye compositions include a two-component oxidative hair dye composition which includes a first part containing an alkali agent, an oxidation dye, and optionally a direct dye such as a nitro dye, and a second part containing an oxidizing agent; and a one-component non-oxidative hair dye composition containing a pH adjusting agent (an acid or an alkali), and at least one direct dye such as an acid dye, a basic dye, and a nitro dye.
The one-component non-oxidative hair dye composition does not contain an oxidizing agent such as hydrogen peroxide, and therefore is advantageous in that the hair dye composition causes less chemical damages to the hair and can be used for hair with a background of various chemical treatments such as hair dyeing treatment or permanent treatment. However, the one-component non-oxidative hair dye composition also has a defect of being poor in shampoo fastness (color durability) as compared with the two-component hair dye composition.
Thus, in order to increase dyeing properties, there have been suggested a technology of accelerating the penetration of a direct dye into the hair using various organic solvents (Patent Document 1), a hair dye pretreatment agent containing L-theanine and a water-soluble polymer (Patent Document 2), or an acidic hair dye pretreatment agent containing urea and benzyl alcohol (Patent Document 3).
The above-mentioned technologies can enhance dyeing properties and at the same time, enhance shampoo fastness. However, enhancing dyeing properties occasionally results in undesirable effects in which the color tone repeatedly changes. Thus, it was essential for their technologies to readjust the color tone.
Meanwhile, as a technology for enhancing shampoo fastness, there has been suggested a post-treatment agent for dyed hair containing a hydroxyalkanesulfonic acid having 2 to 5 carbon atoms, or a salt thereof (Patent Document 4). However, since a combined use with this post-treatment agent makes the treatment more complicated, the method cannot be said to be necessarily a convenient method for dyeing hair, and this method has room for improvement.
Patent Document 1: JP-A-2002-241246
Patent Document 2: JP-A-2007-63199
Patent Document 3: JP-A-2007-126384
Patent Document 4: JP-A-2001-294520